Whenever you see such a problem, think of divisibility issues.
First, rephrase the question: The problem states that 546 is composed of at least 4 factors and also points out to the relationship of those factors (a<b<c<d)
Therefore, start testing the divisibility of 546 with the smallest possible factor (in this case 2). 546/2=273
Then, check if 273 is divisible with 3: 273/3=91 (in case 273 was not divisible with 3, check if it is divisible with 4).
Then, "c" is less than "d" which indicates that you should split 91 among two factors. Check if 91 is divisible with 4, 5, 6 etc.
You will arrive to the conclusion that 91 is divisible with 7 (91/7=13) so c is 7 and d is 13.
This problem involves some "plug-in and play" exercise but if you know the divisibility rules, it is easy.
In conclusion, b+c=3+7=10
My answer is (D).
